Shaft constructions are made in the earth for a number of reasons, including for subaqueous tunneling projects. In these projects, underground tunnels are oftentimes excavated or dug below a body of water such as a river, a lake, a harbor, or a port. The underground tunnels can stretch below the body of water from one side of the body to the other side. Before the tunnels are excavated, a shaft is commonly constructed in the earth down to a vertical depth of tunnel excavation. Shafts are usually constructed at the beginning and at the end of underground tunnels for launching and retrieving excavation equipment and machinery, and for other purposes.
Earth below the surface near these types of shafts, however, tends to be porous and imbued with groundwater and often has a water table relatively close to its surface. The phrase “water table” is customarily used to describe the depth in the earth below the surface at which water pressure head is equal to atmospheric pressure—in simpler terms, it is where the earth below the surface becomes saturated with groundwater. Constructing shafts below water tables can be challenging because the saturated groundwater can easily seep into the shafts. And inflows of groundwater can hinder and sometimes thwart a shaft's usefulness and, in some cases, can ultimately delay the scheduled construction project and increase project costs.